Thread trimming device for lockstitch sewing machine



13, 1969 v F, HANNEMANN ET AL 3,443,540

'THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27,1967 Sheet of 6 INVENTORS," Q

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THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 1967Z of 6 Sheet INVENTORJ:

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THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 1967Sheet 3 of 6' y 1969 F.IHANNEMANN ETAL 3,443,540

THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Fild Feb. 27, 19s?-Sheet 4 of s y 1939 r F. HANNEMANN ET AL 3,443,540

THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27,15567 Sheet FIG.17

May 13, 1969 H MA ETAL 3, 143540 THREAD TRIMMING DEVICE FOR LOCKSTITCHSEWING MACHINE Filed Feb. 27, 1967 Sheet 6 of s United States Patent In.or. Dosb 65/02 US. Cl. 112-252 14 Claims ABSTRACT OF THE DISCLOSURE Adevice for the simultaneous trimming of the needle thread and the bobbinthread underneath a workpiece after the completion of the seam, for usewith lockstitch sewing machines. An arcuate blade oscillatesconcentrically about the looper, and cooperates with a stationary bladecontrolled by the driving and stop means of the sewing machine by meansof cam discs, electromagnets or fluid motors. This device can bealdditionally installed in existing sewing machines without any specialprovision, and can also be used in lockstitch sewing machines providedwith a narrow work-supporting arm and which are further provided in theusual manner with, or are without, an own feed dog device, to be used inautomatic sewing systems, whereby either the :workpiece is directed pastthe sewing machine or the sewing machine is directed past the worpieceby means of a special feeding device.

Background 0 the invention This invention is in the field of US. patentclassification class 112252, entitled, ElementsThread Cutting.

The object of the invention is to provide a thread trimming device,which assures rapid operation, a high degree of security and simplemanipulability, whereat .after trimming the needle and bobbin threadsunderneath the workpiece, the residual thread ends have a short length.

It is a further object of the invention to provide a device which issimple in construction and relatively small in its dimensions.

A further object of the present invention is to enable the device to beadditionally attached to existing machines without demounting essentialdriving members, for instance the looper shaft, and insertion of anadditional operational mechanism into the machine.

It is also an object of the invention to create a thread trimming devicewhich has a small number of mechanical parts. Finally, it is an objectof this invention to dispense with an additional control device forloosening the needle thread tension, required before operation of thethread trimming device.

There are already known devices for trimming both the needle thread andthe bobbin thread after finishing a seam underneath a workpiece. In suchdevices the needle and bobbin threads are trimmed simultaneously by ahooked thread-catch device having a cutting edge and cooperating with afixed knife, whereby the thread-catch device and the fixed knife arearranged below the throat plate and parallel with it.

These thread trimming devices are essentially used with group stitchsewing machines, :which have a control disc for the guided control ofthe feed dog,-the stop mechanism and the thread trimming knives afterengaging the sewing machine for perfonmance of a sewing cycle. Such anarrangement is disclosed in German Patent 417,- 429, issued on J an. 29,1924.

A thread trimming device for lockstitch sewing machines provided with athread-catch device attached to a slidable carrier and cooperating witha fixed knife, whereby the thread-catch device, when in an ineffectiveand rest position is movable into a releasable driving connection withthe looper, is disclosed in German Patent 341,771 of Aug. 22, 1919.

There are also known thread trimming devices employing thread-catchdevices consisting of a ring or segment which envelopes the loopercasing, Whereat the ring is mounted on an oscillating carrier arrangedcoaxially with the looper, said carrier being in releasable drivingconnection with the loop taker shaft.

These devices are disclosed in German Patent No. 353,627 of Sept. 8,1918 and US. Patent No. 3,173,392 to Hedegaand. To cut the threads, thesewing machine has to be stopped initially at the lowest position of theneedle before a starting lever, which couples the actuating shaft of thethread-catch device with the looper-actuating shaft through a geartrain, may be operated.

According to another proposal it is possible to operate said startinglever when the machine is still running. In this construction thestarting impulses is accumulated until the armshaft of the sewingmachine has reached the starting position, in which the thread-catchdevice can come into operation. Such an arrangement is disclosed in US.Patent No. 3,141,432 to Reeber et al.

These known devices require a relatively high amount of mechanicalcoupling and actuating members which, in spite of their location in thesmallest place in an annexaggregate, increase the size of the machine.In addition, the later attachment of such an annex-aggregate to a sewingmachine already at hand is difficult.

Summary According to the invention the objects are solved substantiallyby the provision of a rotating carrier for the trimming blade, wherebythe carrier is in driving connection with a first cam disc drivendirectly or indirectly by the actuating means for the driving and stopmeans of the sewing machine.

Said first cam disc is operably connected with a second cam disc mountedon the rotary feed lifting shaft to influence the action of the firstcam disc for the purpose of drawing off the threads and blocking thethread trimming device and the stitch forming elements.

The cam discs are in driving connection with each other by means of arocker arm having rollers abutting against said cam discs. The rockerarm is pivoted in the bed plate of the sewing machine. The first camdisc which is in driving connection with the carrier for the arcuateblade is pivoted on an axle and is provided with a hollow for receivinga roller pivoted to the rocker arm, in order to keep it out of theeffective range of the second cam disc during the operation of themachine. The second cam disc has a control surface for influencing themovement of this first cam disc. This first cam disc is also providedwith a control surface for the purpose of preventing a jerky drawing offof the bo bbin thread from the bobbin through the arcuate blade, whenperforming a torsional moment to said first disc cam in interaction withboth control surfaces.

The second disc cam is formed with a recess on its control surface forreceiving the roller of the rocker arm. 0n the first cam disc there isprovided a control surface section to impart an accelerated movement tothe arcuate blade during the cutting action, in cooperation with thesecond cam disc.

For driving the first cam disc a rotary magnet, convided for the firstcam disc, for leading it back into its normal position.

However it is also possible to use a lifting magnet or a fluid-motorwhich is in driving connection with the first cam disc and controlled bythe stop mechanism of the sewing machine by means of a lever and a pinattached to the first cam disc.

Below the table plate there may be provided a lever for a direct drivingof the first cam disc, which is provided with a pin and is in drivingconnection with the lever between it and afoot treadle of the drivingmotor, in such a manner that at a backward movement of said foot treadlethe pressure induced by the foot acts elastically upon the first camdisc.

An actuating rod is pivoted on the foot treadle and is in effectiveconnection with a known mechanism for lifting the presser foot and forreleasing the needle thread tension in such a manner, that at a backwardmovement of the foot treadle, first the needle thread tension will beloosened and afterwards the presser foot will be raised. The arcuateblade, attached to the rotating carrier and cooperating with astationary cutting blade, has a baflle attached to the bed plate for thepurpose of assuring a positive application of the trailing age on thearculate blade during cutting off the threads.

Furthermore, the arcuate blade has a groove for the receiving of thethreads during its withdrawal from the thread supply. The groove ends ina clearance and its trailing edge coacts with the stationary cuttingblade. The oscillating carrier for the arcuate blade is cup-shaped andis pivoted in a ball bearing bracket. The bearing bracket houses astuffing for the looper shaft.

In lockstitch sewing machines, provided with a narrow work supportingarm, which do not have their own feed dog, the cam discs and the rockerarm can be placed in the trailing part of the supporting arm, whereatthe driving connection between the cam discs and the oscillating carriercan be effected through an intermediate shaft provided with gear wheels.

Brief description of the drawings FIG. 1 is an elevational view of aframe with a motor and a sewing machine, embodying the presentinvention.

FIG. 2 is a left view of a part of the sewing machine with the trimmingdevice.

FIG. 3 is an enlarged part view of the arcuate blade, stationary cuttingblade and bafile, partially in section.

FIG. 4 is a top plan view of the parts shown in FIG. 3.

FIG. 5 shows the parts of the thread trimming device on the sewingmachine, in nonoperative position.

FIG. 6 shows the thread trimming device at the beginning or the trimmingprocess.

FIG. 7 shows the thread trimming device with the arcuate blade in itsthread-drawing off position.

FIG. 8 shows the device in the thread trimming position.

FIG. 9 is a vertical section taken on line 99 of FIG. 2 with the threadtrimming device being operated through a lever by a lifting magnet, afluid motor or a pedal.

FIG. 10 is a vertical part section taken on line 10--10 of FIG. 11.

FIG. 11 is a view of FIG. 10 in direction of the arrow A.

FIG. 12 is a view of the looper, the carrier for the arcuate blade andits driving means, with the device arranged in a sewing machine having awork supporting arm.

FIG. 13 is a top plan view of the work supporting arm of a lockstitchsewing machine partially in section.

FIG. 14 is a vertical section on line 1414 of FIG. 13.

FIG. 15 is a side elevation of a driving aggregate for the threadtrimming device with a lifting magnet.

FIG. 16 is a side elevation of a driving aggregate including acompressed air motor.

FIG. 17 is a front elevation of a sewing machine, by which the operationof the trimming device, the needle thread tension, the presser foot, andthe motor will be effected through a linkage by means of a edal.

FIG. 18 is a closed schematic view of the linkage and the pedal, seen indirection of the dart B of FIG. 17.

FIG. 19 is a side elevation of an operation device for the threadtrimming device and a linkage for releasing the thread tension and forlifting the presser foot.

FIG. 20 is an enlarged detail of FIG. 19, in front elevation.

Description of the preferred embodiment Referring to FIGS. 1 and 17,there is shown a lockstitch sewing machine having a conventional bedplate 21 supporting an upright 22 carrying an overhanging arm 23 whichterminates in the sewing head 24. Pivoted within the arm 23 is the maindrive shaft 25, operably connected with a reciprocating needle bar 27carrying the needle 26. Secured to the arm drive shaft 25 is a pulley 28driving the loop taker shaft 30 with the looper shaft 32 cooperatingwith the needle 26 and secured to the shaft 30 over a transmission belt29 and a second pully 31 mounted on the looper shaft 30. The looper 32performs in known manner two revolutions during each completeoscillating cycle of the needle 26.

The front end of the looper shaft 30 (FIG. 9) is embraced by an oilretainer 33 mounted in a bearing bracket 34, which is fastened to thebed plate 21 by screws 36. A gasket 35 is interposed between the bedplate 21 and a flange 37 of the bearing bracket 34 having beveledraceways 38 for balls 39, which effects a frictionless pivoting of acup-shaped carrier 40 for an arcuate blade 42 attached to it with screws41.

The balls 39 are disposed in an annular groove 43 profiled in thecarrier 40.

The carrier 40 is formed with a sliding surface 44 with a V-shaped gatefor receiving balls 45. The outer support for the balls 45 is aring-shaped flange 46, having on its tube-formed part 47 a winding 48which is screwed in in the bearing bracket 34. The looper 32, fastenedto the looper shaft 30 by a screw 49, has a recess 50 receiving theflange 46 and the carrier 40. On a section of its circumference thecarrier 40 has a gearing 51 (FIG. 2) for the cooperation with a toothedsector 52 of a cam disc 53.

The cam disc 53, having a prolongation 54, is fitted in a bore 57 on thebed plate 21. The axle 56 is fitted in the bed plate 21 and fastened bya screw 58. Two spring rings 59 on both sides of the cam disc 53 preventits axial movement on the axle 56. On its control face 59' the cam dischas a hollow '60 for receiving a roller 61, pivoted on one end of arocker arm 62. The rocker arm 62 is supported for oscillation on an axle63, fastened to the bed plate 21. The other arm of the rocker arm 62carries a rotating roller 64, which can rest against the control face 65of a cam disc 66, mounted on a rotating shaft, in this case on the feeddog lifting shaft 67.

A coil spring 68 effects the resting of the disc cam 53 with its hollow60 against the roller 61 for the purpose of holding the rocker arm 62and its roller 64 out of the sphere of activity of the cam disc 66during the operation of the sewing machine.

Fastened to the carrier 40 is an arcuate blade 69 (FIGS. 2 to 8) havingtwo points 70, 71, which are directed contrary to in the sense ofrotation of the looper 32. The arcuate blade 69 is reduced in itsthickness towards the points 70, 71. Between the points 70, 71 there isinserted a groove 72 for the needle thread 73 and the bobbin thread 89'.The groove 72 ends in a clearance 74, the trailing edge 75 of whichcooperates with a cutting edge of a stationary cutting blade 77. Thecutting blade 77 and a baffle 78 for the arcuate blade 69 are fastenedby screws 80, 81 to a jib 79 arranged at the bed plate 21.

During a torsional counterclockwise movement, bearing upon the cam disc53, the roller 64 of the rocker arm 62 will be pressed against the camdisc 66. This is effected, after stopping the machine when the needle 26is in its low position, by a lifting magnet 82 through a lever 83 and aroller 84 pivoted to the disc cam 53. (See FIGS. 5, 9 and 15.)

The arcuate blade 69 will have moved to the needle 26 by several angulardegrees. During the movement of the machine caused by rotating the handwheel 85 (FIG. 1) or by a driving motor 86 which is provided with anautomatic stop and rotary device moving the machine which has stopped ina low position of the needle into a position in which the needle 26 isat high position, the roller 64 gets to a control surface 87 of the camdisc 66. After this the roller 61 of the rocker arm 62 is disconnectedfrom the hollow 60, so that in cooperation with a control surface 88 onthe cam disc 53 the arcuate blade 69 with its point 70 may enter thethread triangle formed by the needle thread 73 and may engage the bobbinthread 89' and the needle thread 73 leading to the work piece.

The control surfaces 87 and 88 cooperate with each other over the rockerarm 62 and are shaped in such a manner, that when the bobbin thread 89'is seized by the arcuate blade 69, a jerky drawing off of this threadand consequently an overslipping of the bobbin in its case will beprevented.

The stationary blade 77 is mounted near the stitch-hole to get shortthread ends beneath the work piece 90 after the threads have beentrimmed. On the other hand, the needle thread 73 leading to the needle26 may be cut off proportionally long, to avoid its withdrawal from theneedle 26, when forming the first stitch after trimming.

Also the bobbin thread 89 has to be cut off long enough to get asatisfactory stitch formation at the start. During the drawing off ofthe thread, the needle thread 73 and the bobbin thread 89 FIG. 7, lie inthe groove 72. Immediately before the roller 64 falls into the recess 91(FIG. 8) of the cam disc 66 the threads 73, 89' will be trimmed as thetrailing edge 75, contained in the clearance 74 of the arcuate blade'69, passes by, by the cutting edge 76 of the stationary cutting blade77. After lifting the presser foot 92, the work piece 90 may be removed.Due to the falling of the roller 64 into the recess 91, the sewingmachine is stopped until the cam disc 53 is shifted back into its normalposition (FIG. 5) by means of the coil spring 68 and the releasing ofthe lever 83.

The cam disc 53 may also be driven by a rotary magnet 93, mounted on thebed plate 21 of the machine, FIGS. and 11. The transmission of thetorsional move ment to the cam disc 53 takes place through a gear drive94 on the shaft of the rotary magnet 93 to a toothed sector 95 providedon the cam disc 53.

The cam disc 53 is under tension of a coil spring 96.

A pneumatic drive of the disc cam 53 is shown in FIG. 16. A fluid motor98, controlled by an electromagnetic valve 97, is attached to a plate 99arranged by means of distance pieces 100 on a base plate 101. The baseplate 101 is secured to the table plate 103 by means of screws 102 andcarries, in a bearing 104, the double armed lever 83 for operating thedisc cam 53 over the roller 84. One of the arms of the lever 83 isconnected with the piston rod 106 of the fluid motor 98 over a link 105.A disc 107 is mounted on the piston rod 106 and cooperates with acontact 108 in such a way, that the driving motor 86 can only start whenthe cam disc 53 is in a position shown in FIG. 5.

The operation of the sewing machine for sewing and trimming the threadsis effected by means of a starting and stop device, which consists of afoot treadle 111 (FIG. 1) in the sewing machine 109 with a bed plate 21carried by a frame 110. Two rods 112, 113, FIGS. 1, 19, 20, are linkedto the foot treadle 111, whereat the rod 112 is connected with a shiftlever 114 of the motor 86, while the presser foot rod 113, which is in abushing 115 mounted in an oil tray 116, is connected with the device 117for lifting the presser foot 92 and releasing the needle thread tension118, said device being mounted in the sewing machine 109.

The cranked motor rod 112 (FIG. 20) is slidable supported in a guidebearing 119 pivoted on the foot treadle 111. Screwed to the presser footrod 113, by means of a screw 121, is an entrainment means 120, which isslidably supported on the motor rod 112. Between the olfset part of themotor rod 112 and the entrainment means 120 there is provided a tensionspring 122. The presser foot rod 113 is provided on its upper end with apressure plate 123 for the lifting mechanism of the presser foot 117.

The operation of the above described thread trimming device is asfollows:

By pressing the foot treadle 111 forward from a neutral position theshift lever 114 for engaging the sewing drive will be actuated, wherebythe pressure foot rod 113, resting with its pressure plate 123 on thebushing 115 in the oil tray 116, remains ineffective in the neutralposition, while the tension spring 122 will be stretched. For thepurpose of trimming the threads, the sewing drive will be disconnectedby releasing the foot treadle 111 into the neutral position. By pressingthe foot treadle 111 backwards the needle thread tension 118 will bereleased and then the presser foot 92 will be lifted by means of thepresser foot rod 113 and the device 117 for lifting the presser foot 92and by means of the motor rod 112 and the shift lever 114, the liftingmagnet 82, the rotary magnet 93 or fluid motor 98 and the driving motorwill be switched on. In cooperation with a synchronizing device 124arranged on the main drive shaft 25, FIG. 17, the driving motor 86 willbring the needle 26 into high position during the motional action ofthread trimming already described. By pressing the foot treadle 111further backwards the presser foot 92 will be lifted for removing thework piece.

A direct drive of the cam disc 53 by the starting and stop device of thesewing machine is shown as a further form of construction in FIGS. 17and 18. Apart from the above described rods 112, 113 a further rod 125is required in this construction, the lower end 125 of which is providedwith a collar 127, slidably guided in a tube 126 pivoted on the leftside of the foot treadle 111. On its other end, the rod 125 is slidablyguided in a bushing 128, mounted in the oil tray 116. A plunger with abore 129 is slidably guided on the rod 125. Between the plunger 130 anda setting ring 132 there is arranged a pressure spring 131. Pivoted onthe table plate 103 is a one-armed lever 134 .which rests on the plunger130 and which, as described above, is in effective connection with thecam disc 53 by means of the roller 84.

The operation of this device is as follows:

By pressing the foot treadle 111 forwards the driving motor 86 will becoupled over the motor rod .112 and the shift lever 114. Hereby the tube.126 will slide downwards on to the end 125' of the rod 125, whereby thesetting ring 132 will rest on the bushing 128. After releasing the foottreadle 111 into neutral position, as shown in FIG. 18, the sewingmachine will stop, with the needle 26 in its downward position (FIG. 5).By pressing the foot treadle 11.1 backwards the lever 134 will bepressed against the roller 84 over the setting ring 132, the pressurespring 131 and the plunger 130. A torsional moment will be carried outupon the cam disc 53, as already described. Simultaneously the needlethread tension 118 will be released over the presser foot rod 113 andthe pressure plate 123; the presser foot 92 will be lifted and the shiftlever 1414 of the motor 86 will be operated, through the motor rod .112,thus bringing the needle 26 slowly into high position during thetrimming operation.

It is possible to use a clutch driving motor instead of a positioningmotor. In this case the sewing machine, after disconnecting the drivingmotor 86, may be stopped by hand in a downward position of the needleand by treading the foot treadle 111 backwards and loosening the brakeof the motor, the needle 26 is brought manually into a high positionduring the trimming operation.

In a further form of construction, shown in FIGS. 12 to 14, the threadtrimming device is installed in a work supporting arm sewing machine135, having a proportionally small work supporting arm 136 in its sewingzone. The looper shaft 137, carrying the looper 32, is in drivingconnection with the loop taker drive shaft 138 over a pair of gearwheels 139. The shaft 138 is driven by an arm shaft (not shown) over atoothed belt 140 and a toothed belt wheel 1 41. Secured to the looperdrive shaft 138 is the cam disc 66 provided with the control face 65,against which can abut the roller 64 of the rocker arm 62, pivoted onthe axle 63 mounted in the work supporting arm 136. The other roller 61of the rocker arm 62 is connected with the cam disc 53 formed with atoothed segment 95 and pivoted on the axle 56 fastened in the worksupporting arm 136.

The roller 84, pivoted to the cam disc '53, is positioned adjacent to adouble-armed lever 142 pivoted in the work, supporting arm 136. The onearm of the lever 142 protrudes from the work supporting arm 136 in orderto be operated by the rotary magnet 93, the lifting magnet 82, the fluidmotor 98 or mechanically for transmitting a torsional movement to thecam disc 53. The driving of the carrier 40 with the arcuate blade 42which cooperates with the stationary cutting blade 77 and the bafile 78,is effected by means of an intermediate shaft 143 running parallel tothe looper shaft .137 and carrying two gear wheels 144, 145 whereas thegear wheel 144 mates with the gear wheel 95 of the cam disc 53 and thegear wheel 1'45 mates with the gearing '51 of the carrier 40. A settingring 147 is fastened to the intermediate shaft 143 for taking up one endof a coil spring 147 disposed on the shaft 143. The other end of thecoil spring 147 is held by a wall of the work supporting arm 136.

What we claim is:

1. In combination with a lockstitch sewing machine provided with stitchforming elements including: a reciprocating needle driven by an armshaft, a looper shaft in driven connection with said arm shaft, acylindrical rotatable looper mounted on said looper shaft and providedwith a needle thread seizing beak, a bed plate, a presser foot, a throatplate arranged above said looper within said bed plate, a feed dogwithin said throat plate, means for actuating said feed dog including afeed dog lifting shaft, and a theread tension release for the needlethread: thread trimming means for the needle thread and the looperthreader comprising an arcuate blade, a stationary cutting knifeengageable by said arcuate blade to sever said looper and needle threadswhen said needle is in an upper position, said arcuate blade beingmounted on a carrier pivoted on said looper shaft and arranged in closeproximity to the outer surface of said looper for concentric oscillationabout said looper, driving and stop means for said sewing machine andactuating means for said driving, stop and thread trimming means, saidcarrier being in driven connection with a first cam disc controlled bysaid actuating means, a second cam disc secured to said feed dog liftingshaft and cooperating with said first cam disc for actuating said firstcam disc for drawing off the thrwd from the bobbin, cutting the threadsand blocking the thread trimming means and said stitched formingelements.

2. In the combination as claimed in claim 1, a rocker arm pivoted insaid bed plate and provided with rollers abutting against said camdiscs.

3. The combination claimed in claim 1, wherein said first cam disc is indriven connection with said carrier for said arcuate blade and pivotedon an axle, said first cam disc having a hollow for receiving one ofsaid rollers of said rocker arm to keep it out of the field of action ofsaid second cam disc during the operation of the sewing machine.

4. In the combination as claimed in claim 1, wherein said second camdisc is provided with a control face for influencing the movement ofsaid first cam disc, said first cam disc being provided with a controlface for preventing a jerky drawing off of said bobbin thread from saidbobbin by said arcuate blade while performing a torsional moment to saidfirst cam disc in interaction with said control faces.

5. In the combination as claimed in claim 1, wherein a rocker arm ispivoted in said bed plate and provided with rollers is in operativeconnection with said cam discs, said second cam disc being formed with arecess on its control face for collapsing of one of said rollers intosaid recess, a control face section on said first cam disc for impartingan accelerated movement to said arcuate blade during the cutting actionin cooperation with said second cam disc.

6. In the combination as claimed in claim 1, a rotary magnet for drivingsaid first cam disc, said rotary magnet being controlled by said stopmeans of said sewing machine, a gear drive between said rotary magnetand said first cam disc, said rotary magnet being mounted on said sewingmachine.

7. In the combination as claimed in claim 6, biasing spring means forsaid first cam disc for leading back said cam disc into its normalposition.

8. In the combination as claimed in claim 1, driving means for saidfirst cam disc, a pin secured to said first cam disc and a levercontrolled by said stop means of said sewing machine, said lever beingin driving connection with said pin.

9. In the combination as claimed in claim 1, wherein said first cam discis in driving connection with a lever pivoted below the bed plate ofsaid sewing machine, a foot treadle for the driving motor, a two-piececonnecting rod linking said lever and said foot treadle for varying thepressure upon said first cam disc by moving back said foot treadle.

10. In the combination as claimed in claim 1, wherein said first camdisc is in driving connection with a lever pivoted below the bed plateof said sewing machine, a foot treadle, a two-piece flexible connectingrod between said lever and said foot treadle to actuate said drivingmeans of said sewing machine, to said foot treadle and connected withmeans, for lifting said presser foot and for releasing said needlethread tension by moving backwards said foot treadle, for loosening theneedle thread tension for lifting said presser foot.

11. In the combination as claimed in claim 1, a bafile secured to saidbed plate and cooperating with said arcuate blade for securing theengagement of the knife edge on said arcuate blade during cutting offsaid threads.

12. In the combination as claimed in claim 11, wherein said arcuateblade is provided with a groove for receiving said threads during itswithdrawal from the supply of threads, said groove terminating in aclearance provided with a sharpened edge for cooperating with saidstationary cutting knife.

13. In the combination as claimed in claim 1, wherein said carrier forsaid arcuate blade is of cup-shaped form, a ball-bearing bracket inwhich said carrier is pivoted, an oil retainer arranged in said bearingbracket and surrounding said looper shaft.

14. In combination with a lockstitch sewing machine provided with stitchforming elements including a reciprocating needle driven by an armshaft, a looper shaft in operable connection with said arm shaft, acylindrical rotating looper mounted on said looper shaft and providedwith a needle thread seizing beak, a workpiece supporting arm, a throatplate mounted above said looper within said supporting arm and providedwith a thread tension release for the needle thread: thread trimmingmeans for said needle thread and the looper thread, comprising anarcuate blade, a stationary cutting knife engageable by said arcuateblade to sever said looper and needle threads when said needle is in anupper position, said arcuate blade being mounted on a carrier pivoted onsaid looper shaft and arranged in close proximity to the outer surfaceof said loopers for concentric oscillation about said looper, drivingand stop means for said sewing machine and actuating means for saiddriving, stop and thread trimming device, said carrier being in drivenconnection with a first cam disc controlled by said actuating means, asecond cam disc secured to said looper shaft, a rocker arm provided withrollers, said first cam disc, said second cam disc and said rocker armarranged in the rear part of said supporting arm operably engaging witheach other, an intermediate shaft pivoted in said supporting arm andprovided with gear wheels on each of its ends for meshing with the teethof said carrier and with the teeth of said first cam disc, said rollerspivoted on said rocker arm and abutting against said first and secondcam discs, said rocker arm serving for transferring the rotationalmovements of said first cam disc to said carrier of said arcuate bladein dependence upon the position of said second cam disc, to draw offsaid looper thread from the bobbin, for trimming said threads and forblocking said thread trimming means and said stitch forming elements,

, a biasing spring mounted on said intermediate shaft for returning saidfirst cam disc into its normal position.

References Cited UNITED STATES PATENTS HERBERT F. ROSS, PrimaryExaminer.

